1. Field of the Invention
The present invention relates to a flat multicore wire for use for wiring between flexible printed circuit boards and a method of forming the same wire, and more particularly to a structure for the end portion of such a flat multicore wire and a method of forming the end portion of the same wire.
2. Statement of the Prior Art
There are known a number of types of flat multicore wires, some of which are disclosed in the official gazettes of Japanese Utility Model Laid-Open Nos. 196517/1988, 194413/1988 and so forth. For instance, FIG. 8 shows a flat multicore wire having a conventional structure, and FIG. 8(A) is a plan view of the flat multicore wire, FIG. 8(B) being a front view of the same wire. FIG. 9 also shows another flat multicore wire having a conventional structure, and FIG. 9(A) is a plan view of the flat multicore wire, FIG. 9(B) being a front view of the same wire. FIG. 10 shows still another flat multicore wire having a conventional structure, and FIG. 10(A) is a plan view of the flat multicore wire, FIG. 10(B) being a front view of the same wire.
As shown in FIG. 8, round wires 1 are disposed in parallel in a plate-like fashion with predetermined gaps provided therebetween, and coatings of the end portions of the respective wires are peeled off so as to expose conductors of a certain length. Connecting tapes 5 are applied over the top and bottom surfaces of the coating portions of a group of round wires 1 along the proximal portions of these exposed conductors 2 (hereinafter, simply referred to as a conductor 2) so as to secure the parallel position of the group of wires. Thus, the end portion of the group of wires is constructed such that the conductors 2 act as contact portions for an element that is connected thereto. Moreover, as shown in FIG. 9, in order to prevent bending of the known conductors 2 as shown in FIG. 8, a sheath body 11 for holding a group of conductors 2 together is provided transversely of the conductors 2 at intermediate positions along the length thereof.
In addition, referring to FIG. 10, elongate rectangular conductors 12 for a thin plate or foil body such as an FPC (flexible printed circuit board) or an FFC (flat flexible circuit board) are disposed with predetermined intervals, and are then secured by holding tapes 13 that are applied over the top and bottom surfaces of the same conductors 12 along the full length thereof. Only the top surfaces of the rectangular conductors 12 are exposed at the distal ends thereof over some length so that the exposed portions function as a contact portion 3.
Among the above-described conventional flat multicore wires, in the flat multicore wire shown in FIG. 8, since the rigidity of the conductors 2 projecting in a cantilever-like fashion is in sufficient, the conductors 2 are easy to "bend or buckle" due to resistance generated when a connector is fitted thereover. In order to compensate for the lack of rigidity even to a small extent, wires to be used are limited to tinted wires or solid wires, and thus, since stranded wires are not suitable for use with a flat multicore wire of this type, the flexibility of the entire wires including the contact portion 3 is not good. Thus, the flat multicore wire shown in FIG. 8 has the drawback that it is not suitable for use a moving portion where a connection include a bend, or where wires are repeatedly bent at an intermediate position along the length thereof.
Furthermore, in the flat multicore wire as shown in FIG. 9 in which the rigidity of the conductors 2 is intended to be improved, although the above-mentioned bending or buckling of the conductors is prevented, since the conductors 2 are inserted into a connector together with the sheath body 11, a great magnitude of insertion force is required, resulting in a low operating efficiency. In particular, since the resin sheath body 11 becomes hard in winter when the temperature becomes low, the efficiency with which the conductors 2 are inserted into a connector remarkably decreases.
In contrast, in the flat multicore wire as shown in FIG. 10, since the conductors themselves are each formed into a rectangular shape, the flexural rigidity relative to the transverse direction is high, and therefore there is no "bending or buckling" of the conductors that would be caused when the conductors are inserted into a connector. However, since the holding tapes 13 are applied to the top and bottom surfaces of a group of rectangular conductors 12 along the full length thereof, the flexural rigidity of the entire wires relative to the transverse direction becomes high, and therefore the flat multicore wire in FIG. 10 suffers from the drawback that it is not suitable for a two-dimensional application. Moreover, it has another drawback that the rectangular conductors 12 cannot be arranged together using sealed wires.